1. Field of the Invention
The present invention relates to a method and to an apparatus for coating workpieces through the intermediary of a chemical, heterogeneous vapor-phase reaction in a dynamic process, in which reactants are introduced into a reaction chamber, and a gas or gas-vapor mixture is withdrawn from the reaction chamber.
2. Discussion of the Prior Art
Currently known prior art methods which relate to coating processes through separation from the vapor phase employ static and dynamic processes. The static method; for example as disclosed in German Laid-open Patent Application No. 24 37 876 merely describes positioning the workpiece which is to be coated in a hermetically-sealed reaction atmosphere under a definite temperature. The composition as defined by the reaction atmosphere is hereby provided either once in the quantity which is required to form the coating, or supplied repeatedly at predetermined intervals. Although this process is carried out in proximity to the reaction equilibrium which is required for the separation, it necessitates a relatively lengthy reaction period and, at best, is suitable only for small workpieces.
When employing the principle of the dynamic method, such as described, for example, in U.S. Pat. No. 3,684,585, the gas-vapor mixture which is required for the coating is introduced in a suitable concentration into a reaction furnace containing the workpiece which is to be coated. Therein, the mixture reacts with the surface of the workpiece, and exits into the environment with a correspondingly changed composition. In this process there is achieved a much shorter reaction period than with the static method. In order to produce qualitatively good coatings, through suitable monitoring of the addition of reactants to the process there must be achieved the reaction equilibrium process, which necessitates extensive control requirements. Moreover, the dynamic process requires a relatively high consumption of material.